Thread take-up mechanism for a sewing machine



March 20, 1962 KElKlCHl EBIHARA ETAL 3,025,810

THREAD TAKE-UP MECHANISM FOR A SEWING MACHINE 2 Sheets-Sheet 2 Filed July 27, 1959 United States Patent 3,025,810 THREAD TAKE-UP MECHANISM FOR A SEWING MACHINE Keikichi Ebihara, 116 Minami-Senzoku-cho, Ota-ku, and

Kiyoshi Ogawa, 521 Kamitakaido 3-chome, Suginamiku, both of Tokyo, Japan Filed July 27, 1959, Ser. No. 829,561 Claims priority, application Japan Aug. 8, 1958 1 Claim. (Cl. 112-241) This invention relates to a thread take-up mechanism for a sewing machine, comprising six-bar linkage having pivot points only, and has for its object to provide an improved thread take-up lever having its free end adapted to perform an ideal thread take-up motion. Another object is to provide a noiseless thread take-up mechanism for a sewing machine.

The accompanying drawing will serve to illustrate specific embodiment of our invention, in order that its utility and functioning will be thoroughly appreciated. It will be understood, however, that this is by way of illustration only and is not to be taken as limiting the invention in any way.

In the drawing:

FIGURE 1 shows a displacement diagram obtained from conventional grooved cam type and four-bar linkage type thread take-up mechanisms;

FIGURE 2. is a sectional front view of the thread take-up mechanism constructed according to the present invention;

FIGURE 3 is a side view thereof, and

FIGURE 4 shows a displacement diagram obtained from the thread take-up linkage mechanism according to the present invention.

In a conventional type of thread take-up mechanism comprising a grooved cam, it is noted that the mechanism performs an ideal and perfect thread take-up motion. In such type of mechanism, however, it is observed that the operation is considerably noisy and undue wear of the sliding parts is unavoidable, due to the fact that the grooved cam and the thread take-up lever roller engaging therewith form a higher pair. On the other hand, a conventional four-bar linkage mechanism is adapted to operate smoothly without producting any undue noise, and it is adapted for longer use as compared with the aforementioned grooved cam type thread take-up mechanism. It is observed, however, that in such type of mechanism the free end of the thread take up lever does not perform the ideal thread take-up motion.

In the diagram shown in FIGURE 1, the full line curve a designates the displacement of the free end of the thread take-up lever of a cam type thread take-up mechanism designed and constructed ideally, and the dotted line curve b designates similar displacement obtained from a four-bar linkage type thread take-up mechanism. As will be seen from said diagram, with respect to the four-bar linkage mechanism the building-up curve is not so steep, exceeding 100 as shown by the curve 23', as compared with the ideal building-up curve 1-23 in the displacement curve a, the latter not exceeding 100 and in the specific example shown extending for about 97", which is the most preferable condition. Moreover, in the curve b, there is not a rest position at all corresponding to the rest position 56 found in the displacement curve a. This lack of the rest position in the displacement curve b would result in insufficient tensioning of the thread during stitching. With respect to the four-bar linkage, in order to bring the building-up curve 12-3 of the displacement curve b in conformity with the building-up curve 12-3 of the displacement curve a of the cam type thread take-up mechanism, the point 1 must be displaced to the left ICC from the point 1 so as to bring the point 3' nearer toward the point 3 as shown in FIGURE 1, attempting to make the ideal displacement curve. By this, on the other hand, the distance between 1 and 1' becomes larger, which is not desirable for the reason of slackening of the thread. The most important drawback of the fourbar linkage type mechanism is the lack of the rest position 5-6 in the displacement curve, as hereinbefore described.

Now, referring to FIGURES 2 and 3, showing the thread take-up mechanism according to the present invention, there is provided a six-bar linkage having pivot points, the six-bar linkage consisting of the link M M (fixed link), M,,A (driver), AFD (intermediate link), DE (intermediate link), FG (intermediate link), and EM GC (follower). If any one of the said six links were omitted, the follower link would perform a free or arbitrary motion and the desired periodic motion would not be obtained. When the driving link M,,A secured to the upper shaft M of the sewing machine is rotated, the motion is transmitted to the first intermediate link AFD connected by the pivot point A, the second intermediate link DE connected by two pivot points D and F, and the third link PG, and then to the follower EM GC (thread take-up lever) which is oscillatable around the pivot point M secured to the machine arm body, through the pivot points E and G, thus the latter link M GC performing the ideal and perfect thread take-up motion.

In the diagram shown in FIGURE 4, the thick line curve 0 designates the displacement of the free end C of the thread take-up lever of the mechanism according to this invention. In the diagram, the displacement curves a and b for the grooved cam type and the fourbar linkage type thread take-up mechanisms, respectively, are shown for the sake of comparison. It will be noted that with respect to the thick line curve c the building-up curve terminates at a point within and that there is found the desired rest position.

Heretofore it has been considered that the accuracy of the thread take-up mechanism would be decreased as the number of links is increased. Contrary to such consideration, in the mechanism according to the present invention, its function is considerably stable due to the fact that the follower link is oscillatable around the axis of pivot point M rigidly secured to the body of the machine, in contrast with the old four-bar linkage type mechanism, in which the point of thread take-up lies on a point in the intermediate link. The accuracy of the thread take-up mechanism according to the present invention is by no means decreased as compared with the existing four-bar linkage mechanism.

From the foregoing, it will be noted that according to the present invention in which is employed six-bar linkage system having only pivot points it is possible to remove the drawbacks inherent to the existing four-bar linkage system, obtaining the ideal displacement curve as shown and attaining the most silent operation.

What we claim is:

An improved thread take-up mechanism for porperly tensioning the thread during stretching, arranged in the body of a sewing machine, said body having an upper drive shaft with a longitudinal center axis, and said improved thread take-up mechanism comprising, a fixed link defined by body structure between the longitudinal center axis of the upper driving shaft and a fixed pivot point on said body, a driving link defined between the center axis of the drive shaft and an eccentric pivot point positioned off-center on the drive shaft, a first intermediate link pivotably connected at one end to the eccentric pivot point on the drive shaft and defining pivot points respectively at its other end and between said ends,

a second intermediate link pivotably connected at one end to the pivot point defined by the other end of said first intermediate link, and said second intermediate link defining a pivot point at its other end, a third intermediate link pivotably connected at one end to the pivot point between the end pivot points defined by said first intermediate link, and a follower link comprising a bell-crank shaped thread take-up lever having a short and a long arm and defining pivot points at the free end of the short arm, at the angle between the arms and between said angle and the free end of the long arm, said take-up lever pivotably connected at the pivot point defined at said angle to said body at said fixed pivot point thereon, the free end of said short arm being pivotably connected to the other end of said second intermediate link and the long arm being pivotably connected at the pivot point defined thereon to the free end of said third intermediate link, whereby said upper drive shaft noiselessly operates said thread take-up lever and causes the free end of its long arm to oscillate about said angle pivot point with a motion in which said free end is approximately motionless at a point approximately midway between points of maximum displacement of said free end, thereby providing a six link linkage pivotably joined at pivot points by pivots only.

References Cited in the file of this patent UNITED STATES PATENTS 718,708 Diehl Jan. 20, 1903 1,402,930 Herr Jan. 10, 1922 2,188,228 Mueller Jan. 23, 1940 

